The present invention relates to an ink jet head and an ink jet recording apparatus.
An ink jet head using piezoelectric actuators including piezoelectric elements with electrodes provided on both sides thereof is known in the art, as disclosed in Japanese Laid-Open Patent Publication No. 2001-162794. An ink jet head of this type includes a plurality of nozzles, a plurality of pressure chambers associated with the respective nozzles, and a plurality of piezoelectric actuators associated with the respective pressure chambers. Typically, a single xe2x80x9ccommon electrodexe2x80x9d is provided on one side of the plurality of piezoelectric actuators so that the common electrode is shared by the piezoelectric actuators. On the other hand, xe2x80x9cseparate electrodesxe2x80x9d are provided independently on the other side of the plurality of piezoelectric actuators. With the ink jet head as described above, a voltage is applied between a separate electrode and the common electrode so as to expand/contract a piezoelectric element, and a pressure is applied on the ink in a pressure chamber by the expansion/contraction, thereby discharging the ink through a nozzle.
An ink jet head is provided with a driving circuit for supplying a driving signal. The driving circuit of a conventional ink jet head has the same number of channels as the number of actuators in order to supply a driving signal individually to the separate electrode of each actuator. The driving circuit is designed so that a pulse signal is applied to an actuator that is to discharge ink while a pulse signal is not applied to an actuator that is not to discharge ink, thus turning the signal ON/OFF individually for each actuator.
With such an ink jet head, however, as the number of actuators increases, the number of channels of the driving circuit increases accordingly, whereby the cost for the driving circuit increases inevitably. With the recent increase in the number of nozzles provided in an ink jet head, the increase in the cost for the driving circuit is becoming non-negligible.
In view of this, an ink jet head employing a so-called xe2x80x9cmatrix drivingxe2x80x9d method has been suggested in the art, in which scanning electrodes and counter electrodes are arranged in a matrix pattern, as disclosed in Domestic Republication of PCT Publication WO99/12739. With an ink jet head employing a matrix driving method, the number of channels of the driving circuit can be reduced significantly, and thus the cost for the driving circuit can be reduced.
In an ink jet head employing a matrix driving method as described above, relay terminals connecting the driving circuit with the scanning electrodes, and relay terminals connecting the driving circuit with the counter electrodes, are localized at corners of the head assembly.
As a result, scanning electrode lead wires connecting the relay terminals with the scanning electrodes, and counter electrode lead wires connecting the relay terminals with the counter electrodes, are relatively long. Therefore, the lead wires have relatively high electric resistances.
Moreover, the scanning electrode lead wires and the counter electrode lead wires have different lengths for different scanning electrodes or different counter electrodes. Therefore, signals supplied to different electrodes vary slightly from one another, whereby different nozzles are likely to have varied levels of ink discharging performance. As a result, the recording precision is not sufficiently high. Moreover, while it is necessary, with a matrix driving method, that signals to be applied to the scanning electrodes (hereinafter referred to as xe2x80x9cscanning signalsxe2x80x9d) and signals to be applied to the counter electrode (hereinafter referred to as xe2x80x9crecording signalsxe2x80x9d) need to be precisely synchronized with each other, it is difficult to achieve precise synchronization if signals supplied to different electrodes vary from one another.
Some ink jet heads use a plurality of types of ink. For example, an ink jet head for forming a color image uses a plurality of colors of ink. In such an ink jet head, a plurality of actuators are provided to form a column of actuators for each color. With a conventional ink jet head of this type, the driving circuit supplies the same driving signal to actuators of the actuator columns for all colors.
However, properties of ink such as the viscosity vary among different types of ink. Therefore, even if the same driving signal is applied, the difference in the type of ink results in a difference in the ink discharging performance.
In view of this, in the prior art, types of ink are chosen, or the physical properties of different types of ink are adjusted, so that the ink discharging characteristics are made uniform among the different types of ink. However, this imposes a certain limitation on the types of ink that can be used.
Another way is to adjust a driving signal for each type of ink. However, with such an ink jet head, as disclosed in Japanese Laid-Open Patent Publication No. 2001-162794, the configuration of the driving circuit may become complicated, leading to other problems such as an increase in the cost for the driving circuit and a decrease in the reliability in controlling the ink discharge.
Note that these problems occur not only when a plurality of types of ink are used, but also when there are variations in the actuator characteristics or the pressure chamber size among different actuator columns.
The present invention has been made in view of the above. An object of the present invention is to shorten a lead wire connecting a relay terminal with an electrode. Another object of the present invention is to suppress the variations among signals supplied to different electrodes, thereby improving the ink discharging performance. Still another object of the present invention is to precisely synchronize the scanning signal with the recording signal. Yet another object of the present invention is to provide a technique that allows easy adjustment of a driving signal for each column without complicating the configuration of the driving circuit.
An ink jet head of the present invention includes: a head assembly provided with a plurality of nozzles and a plurality of pressure chambers storing ink therein and communicated respectively to the nozzles; actuators each associated with one of the pressure chambers and each including a piezoelectric element, a scanning electrode provided on one side of the piezoelectric element, and a recording electrode provided on the other side of the piezoelectric element, wherein the actuators are arranged in a matrix pattern of n rows by m columns (where n and m are natural numbers equal to or greater than two) in terms of electrical circuit, with the recording electrodes of each row being electrically connected to one another, and the scanning electrodes of each column being electrically connected to one another; and a driving circuit for supplying a scanning signal to the scanning electrodes for each column, while supplying a recording signal to each row of the recording electrodes in synchronization with the scanning signal, wherein: the actuators are geometrically arranged in n rows by m columns on the head assembly; a relay terminal, extending in a vertical direction, is provided in at least one inter-column space between vertical columns of the actuators on the head assembly for relaying signals from the driving circuit to the recording electrodes and the scanning electrodes; and the recording electrodes and the scanning electrodes are connected to the relay terminal via lead wires extending in a horizontal direction.
In this ink jet head, the relay terminal extends in the vertical direction, and the lead wires connecting the relay terminal with the recording electrodes and the scanning electrodes extend in the horizontal direction, whereby it is not necessary to extend the lead wires in a complicated pattern, e.g., a meandering pattern, and it is thus possible to reduce the length of the lead wires. Moreover, since the relay terminal is provided in an inter-column space between actuator columns, the distance between the relay terminal and the actuators is reduced, whereby the length of the lead wires can be reduced accordingly.
It is preferred that m is an even number; and the relay terminal is provided in a central inter-column space between the actuators.
This allows for a further reduction of the length of the lead wires. Moreover, the arrangement pattern of the lead wires is left-right symmetrical with respect to the relay terminal, thereby reducing variations between signals supplied to the electrodes of the left-side actuators and those supplied to the electrodes of the right-side actuators, and thus suppressing variations in the ink discharging performance. Moreover, the scanning signal and the recording signal can be synchronized with each other more precisely.
Another ink jet head of the present invention includes: the head assembly; the actuators; and the driving circuit, wherein: a first relay terminal and a second relay terminal, both extending in a vertical direction, for relaying signals from the driving circuit to the recording electrodes and the scanning electrodes are provided on a left side and a right side, respectively, of an area on the head assembly where the actuators are arranged; and the recording electrodes and the scanning electrodes are connected to the relay terminals via lead wires extending in a horizontal direction.
Also in this ink jet head, the relay terminals extend in the vertical direction, and the lead wires connecting the relay terminals with the recording electrodes and the scanning electrodes extend in the horizontal direction, whereby it is not necessary to extend the lead wires in a complicated pattern, e.g., a meandering pattern, and it is thus possible to reduce the length of the lead wires. Moreover, the relay terminal is divided into two relay terminals, which are provided on the left side and the right side of the area where the actuators are arranged, whereby the distance between each relay terminal and the actuators associated with the relay terminal is reduced, whereby the length of the lead wires can be reduced accordingly.
It is preferred that m is an even number; the recording electrodes and the scanning electrodes of the actuators on the left side are connected to the first relay terminal; and the recording electrodes and the scanning electrodes of the actuators on the right side are connected to the second relay terminal.
This allows for a further reduction of the length of the lead wires. Moreover, the arrangement pattern of the lead wires is left-right symmetrical, thereby reducing variations between signals supplied to the electrodes of the left-side actuators and those supplied to the electrodes of the right-side actuators, and thus suppressing variations in the ink discharging performance. Moreover, the scanning signal and the recording signal can be synchronized with each other more precisely.
It is preferred that a difference in time constant between actuators belonging to different vertical columns is set to be 0.1 xcexcs or less.
In one embodiment, an actuator that is geometrically located along a pth row and a qth column (where p is a natural number of 1 to n, and q is a natural number of 1 to m) is located along the pth row and the qth column in terms of electrical circuit.
In this ink jet head, the arrangement pattern of the actuators in terms of electrical circuit coincides with the geometric arrangement pattern thereof
In one embodiment, actuators that are geometrically adjacent to each other in the vertical direction belong to different columns in terms of electrical circuit.
The scanning signal is supplied separately for each column, and the scanning signal will not be supplied simultaneously to actuators belonging to different columns. Therefore, with this ink jet head, actuators that are geometrically adjacent to each other in the vertical direction will not be driven at the same time. Thus, it is possible to prevent crosstalk between actuators that are adjacent to each other in the vertical direction, thereby improving the ink discharging performance.
In one embodiment, actuators that are geometrically adjacent to each other in the horizontal direction belong to different columns in terms of electrical circuit.
In this way, it is possible to prevent crosstalk between actuators that are adjacent to each other in the horizontal direction, thereby improving the ink discharging performance.
In one embodiment, actuators that are geometrically adjacent to each other in the vertical direction and those that are geometrically adjacent to each other in the horizontal direction belong to different columns in terms of electrical circuit.
In this way, it is possible to prevent crosstalk between actuators that are adjacent to each other in the vertical direction and those that are adjacent to each other in the horizontal direction, thereby improving ink discharging performance.
In one embodiment, a driving signal obtained by combining the recording signal with the scanning signal varies among at least two or more actuator columns.
In this way, the voltage of the driving signal can be adjusted for each column, and it is possible to control the ink discharge for each column according to the actuator characteristics, the ink characteristics, etc., of the column.
In one embodiment, a voltage of the scanning signal is equal among different actuator columns; and a voltage of the recording signal varies among at least two or more actuator columns.
In one embodiment, a voltage of the recording signal is equal among different actuator columns; and a voltage of the scanning signal varies among at least two or more actuator columns.
In one embodiment, a voltage of the scanning signal varies among at least two or more actuator columns; and a voltage of the recording signal varies among at least two or more actuator columns.
In one embodiment, when ink is to be discharged, a driving signal obtained by combining the recording signal with the scanning signal includes an ink discharging pulse signal for driving an actuator so as to discharge ink and an auxiliary pulse signal for driving an actuator to such a degree that ink is not discharged, and when ink is not to be discharged, the driving signal includes the auxiliary pulse signal for driving an actuator to such a degree that ink is not discharged.
Thus, by driving an actuator to such a degree that ink is not discharged by using the auxiliary pulse signal, it is possible to, for example, suppress the residual vibration after ink is discharged, or suppress an increase in the viscosity of ink in the nozzle.
In one embodiment, a voltage of the auxiliary pulse signal varies among at least two or more actuator columns.
In this way, the voltage of the auxiliary pulse signal can be adjusted for each actuator column, and it is possible to supply the auxiliary pulse signal for each column according to the actuator characteristics, the ink characteristics, etc., of the column.
In one embodiment, the ink discharging pulse signal is included in the recording signal; and the auxiliary pulse signal is included in the scanning signal.
In this way, with respect to the production of the driving signal, the recording signal and the scanning signal can be simplified.
It is preferred that the driving circuit supplies, prior to a recording operation, a preliminary pulse signal for driving an actuator to such a degree that ink is not discharged to all actuators.
Before a recording operation, ink in a nozzle may be dry and have an increased viscosity. If the viscosity of ink in a nozzle is high, a false discharge of ink may occur through the nozzle. However, with this ink jet head, the preliminary pulse signal is supplied prior to the recording operation, thereby stirring ink in the nozzle. Therefore, a portion of ink of a high viscosity near the exit of a nozzle is mixed with a portion of ink of a low viscosity inside the nozzle, thereby suppressing the increase in the viscosity of ink. Thus, it is possible to prevent the false discharge of ink at the start of a recording operation.
In one embodiment, when a small ink droplet is to be discharged, a driving signal obtained by combining the recording signal with the scanning signal includes a first pulse signal, and when a large ink droplet is to be discharged, the driving signal includes two or more pulse signals produced after the first pulse signal.
In this way, a small ink droplet is discharged when a single pulse signal is supplied, and a large ink droplet is discharged when a plurality of pulse signals are supplied. A large ink droplet is discharged by a so-called xe2x80x9cmulti-pulsexe2x80x9d driving method. This allows for a multi-gray-level recording operation. In a case where a small ink droplet and a large ink droplet are discharged successively, the first pulse signal for discharging a small ink droplet is supplied after the supply of a plurality of pulse signals for discharging a large ink droplet in the preceding cycle. If the plurality of pulse signals and the first pulse signal are discharged successively, the discharge of a small ink droplet is likely to be influenced by the residual vibration of the actuator from the discharge of a large ink droplet. However, with this ink jet head, the scanning signal is supplied separately for each column, whereby there is a certain time interval corresponding to the number of actuator columns between the discharge of a large ink droplet and the discharge of a small ink droplet. Therefore, the discharge of a small ink droplet after the discharge of a large ink droplet is less likely to be influenced by the residual vibration and can be done stably.
In one embodiment, the n rows by m columns of actuators are geometrically arranged on the head assembly so that at least actuators of vertical columns that are adjacent to each other, among m vertical columns each including n actuators arranged in the vertical direction, are shifted from each other with respect to the vertical direction.
In one embodiment, the actuators are geometrically arranged in a staggered pattern on the head assembly.
Still another ink jet head of the present invention includes: the head assembly; the actuators; the driving circuit, wherein a voltage of a driving signal obtained by combining the scanning signal with the recording signal varies among at least two or more actuator columns.
In this way, the driving signal is obtained by combining the scanning signal with the recording signal, whereby it is no longer necessary to produce a plurality of driving signals for different actuators. Therefore, without complicating the driving circuit, the voltage of the driving signal can be adjusted for each actuator column, and it is possible to easily supply the driving signal for each column according to the actuator characteristics, the ink characteristics, etc., of the column.
In one embodiment, a voltage of the scanning signal is equal among different actuator columns; and a voltage of the recording signal varies among at least two or more actuator columns.
In one embodiment, a voltage of the recording signal is equal among different actuator columns; and a voltage of the scanning signal varies among at least two or more actuator columns.
In one embodiment, a voltage of the scanning signal varies among at least two or more actuator columns; and a voltage of the recording signal varies among at least two or more actuator columns.
In one embodiment, when ink is to be discharged, the driving signal includes an ink discharging pulse signal for driving an actuator so as to discharge ink and an auxiliary pulse signal for driving an actuator to such a degree that ink is not discharged, and when ink is not to be discharged, the driving signal includes the auxiliary pulse signal for driving an actuator to such a degree that ink is not discharged; and a voltage of the ink discharging pulse signal varies among at least two or more actuator columns.
Thus, by driving an actuator to such a degree that ink is not discharged by using the auxiliary pulse signal, it is possible to, for example, suppress the residual vibration after ink is discharged, or suppress an increase in the viscosity of ink in the nozzle. By adjusting the voltage of the ink discharging pulse signal for each actuator column, it is possible to discharge ink for each column according to the actuator characteristics, the ink characteristics, etc., of the column.
In one embodiment, when ink is to be discharged, the driving signal includes an ink discharging pulse signal for driving an actuator so as to discharge ink and an auxiliary pulse signal for driving an actuator to such a degree that ink is not discharged, and when ink is not to be discharged, the driving signal includes the auxiliary pulse signal for driving an actuator to such a degree that ink is not discharged; and a voltage of the auxiliary pulse signal varies among at least two or more actuator columns.
Thus, the auxiliary pulse signal provides auxiliary driving of an actuator such that ink is not discharged. As a result, it is possible to, for example, suppress the residual vibration after ink is discharged, or suppress an increase in the viscosity of ink in the nozzle. By adjusting the voltage of the auxiliary pulse signal for each actuator column, it is possible to provide auxiliary driving for each column according to the actuator characteristics, the ink characteristics, etc., of the column.
In one embodiment, the ink discharging pulse signal is included in the recording signal; and the auxiliary pulse signal is included in the scanning signal.
In this way, with respect to the production of the driving signal, the recording signal and the scanning signal can be simplified.
In one embodiment, when a small ink droplet is to be discharged, the ink discharging pulse signal includes a first pulse signal, and when a large ink droplet is to be discharged, the ink discharging pulse signal includes two or more following pulse signals produced after the first pulse signal.
In one embodiment, the driving circuit supplies, prior to a recording operation, a preliminary pulse signal for driving an actuator to such a degree that ink is not discharged to all actuators.
An ink jet recording apparatus of the present invention includes: any of the ink jet heads set forth above; and movement means for relatively moving the ink jet head and a recording medium with respect to each other.